C-reactive protein: the difference between quantitation is serum and EDTA plasma

Area of Science:

• Clinical Chemistry
• Biochemistry
• Laboratory Medicine

Background:

• Accurate C-reactive protein (CRP) quantitation is crucial for diagnosing and monitoring inflammation.
• Variations in sample matrices, such as serum versus EDTA plasma, can impact assay results.
• Understanding these matrix effects is essential for reliable clinical interpretation.

Purpose of the Study:

• To investigate and quantify the discrepancies in C-reactive protein (CRP) measurements using EDTA plasma versus serum.
• To evaluate the effect of K3-EDTA addition on CRP assay performance in different sample types.
• To explore potential mechanisms underlying observed matrix effects in CRP turbidimetric assays.

Main Methods:

• Turbidimetric assay for C-reactive protein (CRP) quantitation.
• Comparative analysis of results obtained from EDTA plasma and serum samples.
• Assessment of CRP assay performance with and without the addition of K3-EDTA to the reaction buffer.

Main Results:

• A systematic discrepancy was observed between serum and EDTA plasma CRP values, particularly at low concentrations (<20 mg/L).
• Serum generally showed lower CRP values than EDTA plasma at low concentrations, and slightly higher values at high concentrations.
• Addition of K3-EDTA to serum samples normalized CRP values, revealing an overall ~8% lower result in EDTA plasma compared to serum.
• Differential water content between serum and plasma is proposed as the primary cause for these discrepancies.

Conclusions:

• The choice of sample matrix (serum vs. EDTA plasma) significantly influences C-reactive protein (CRP) quantitation results.
• K3-EDTA addition to serum assays enhances sensitivity and helps standardize CRP measurements, mitigating matrix-related discrepancies.
• Further investigation into the role of EDTA and water content is warranted to fully elucidate CRP assay behavior.